Enforce constant size and device scale factor for surfaces

content/renderer/android/synchronous_compositor_frame_sink.cc

Index: content/renderer/android/synchronous_compositor_frame_sink.cc
diff --git a/content/renderer/android/synchronous_compositor_frame_sink.cc b/content/renderer/android/synchronous_compositor_frame_sink.cc
index be2a84041928de80e7d66ef149aa80ba0da4fddb..1da0d84f7b2b818efbe7db0d4b8c092d587da9c6 100644
--- a/content/renderer/android/synchronous_compositor_frame_sink.cc
+++ b/content/renderer/android/synchronous_compositor_frame_sink.cc
@@ -242,14 +242,6 @@ void SynchronousCompositorFrameSink::SubmitCompositorFrame(
     // the |frame| for the software path below.
     submit_frame.metadata = frame.metadata.Clone();
 
-    if (!root_local_surface_id_.is_valid()) {
-      root_local_surface_id_ = local_surface_id_allocator_->GenerateId();
-      child_local_surface_id_ = local_surface_id_allocator_->GenerateId();
-    }
-
-    display_->SetLocalSurfaceId(root_local_surface_id_,
-                                frame.metadata.device_scale_factor);
-
     // The layer compositor should be giving a frame that covers the
     // |sw_viewport_for_current_draw_| but at 0,0.
     gfx::Size child_size = sw_viewport_for_current_draw_.size();
@@ -261,6 +253,23 @@ void SynchronousCompositorFrameSink::SubmitCompositorFrame(
                            sw_viewport_for_current_draw_.bottom());
     display_->Resize(display_size);
 
+    if (!root_local_surface_id_.is_valid() || display_size_ != display_size ||
+        device_scale_factor_ != frame.metadata.device_scale_factor) {
+      root_local_surface_id_ = local_surface_id_allocator_->GenerateId();
+      display_size_ = display_size;
+      device_scale_factor_ = frame.metadata.device_scale_factor;
+    }
+
+    if (!child_local_surface_id_.is_valid() || child_size_ != child_size ||
+        device_scale_factor_ != frame.metadata.device_scale_factor) {
+      child_local_surface_id_ = local_surface_id_allocator_->GenerateId();
+      child_size_ = child_size;
+      device_scale_factor_ = frame.metadata.device_scale_factor;
+    }
+
+    display_->SetLocalSurfaceId(root_local_surface_id_,
+                                frame.metadata.device_scale_factor);
+
     // The offset for the child frame relative to the origin of the canvas being
     // drawn into.
     gfx::Transform child_transform;
@@ -274,6 +283,8 @@ void SynchronousCompositorFrameSink::SubmitCompositorFrame(
     // hardware frames in SurfacesInstance?)
     cc::CompositorFrame embed_frame;
     embed_frame.metadata.begin_frame_ack = frame.metadata.begin_frame_ack;
+    embed_frame.metadata.device_scale_factor =
+        frame.metadata.device_scale_factor;
     embed_frame.render_pass_list.push_back(cc::RenderPass::Create());
 
     // The embedding RenderPass covers the entire Display's area.